1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly to a color filter substrate with an improved spacer structure for a liquid crystal display.
All of patents, patent applications, patent publications, scientific articles and the like, which will hereinafter be cited or identified in the present application, will, hereby, be incorporated by references ill their entirety in order to describe more fully the state of the art, to which the present invention pertains.
2. Description of the Related Art
A conventional structure of a liquid crystal display with a color filter substrate including column-shaped spacers will be described with reference to the drawings. FIG. 1A is a fragmentary schematic plan view of a conventional structure of a color filter substrate included in a conventional liquid crystal display. FIG. 1B is a fragmentary schematic cross sectional elevation view, taken along an X-X′ line in FIG. 1A, illustrative of the conventional structure of the conventional liquid crystal display.
The liquid crystal display includes a color filter substrate 111 and a thin film transistor substrate 131 as well as a liquid crystal layer 113 filling in an inter-space between the color filter substrate 111 and the thin film transistor substrate 131.
The thin film transistor substrate 131 has a normal structure which includes a glass substrate, an insulating film, a matrix array of thin film transistors, interconnections and an orientation film which are not illustrated.
The color filter substrate 111 has a matrix array of pixels, each of which includes a set of primary-three-color filters 123, 124 and 125 which extend in parallel to each other and in a horizontal direction perpendicular to the X—X′ line in FIG. 1A. The each pixel is represented by a broken line in FIG. 1A and has a rectangle shape in plan view which has a longitudinal direction along the X—X′ line in FIG. 1A.
With reference to FIG. 1B, the color filter substrate 111 includes a glass substrate 101, a black matrix layer 102, color filter layers 123, 124 and 125, a common electrode layer 106, a column-shaped spacer 143, and an orientation film 107. The black matrix layer 102 extends over the glass substrate 101. The color filter layers 123, 124 and 125 extend over the black matrix layer 102 in the horizontal direction perpendicular to the X—X′ line. The color filter layers 123, 124 and 125 are aligned in the direction along the X—X′ line at a constant pitch and a constant gap, so that parts of the top surface of the black matrix layer 102 are exposed. Each of the color filter layers 123, 124 and 125 has a ridge shape in sectioned view, so that each of the color filter layers 123, 124 and 125 has a top plat surface and two sloped side-walls. The common electrode layer 106 extends on the top plat surface and the two sloped side-walls of the color filter layers 123, 124 and 125 and also on the exposed surface of the black matrix layer 102. The common electrode layer 106 may typically comprise an indium tin oxide film.
The column-shaped spacer 143 is provided in a gap between adjacent two of the pixels. The column-shaped spacer 143 is provided on the common electrode layer 106 over the top flat surface of the color filter layer 123. The orientation film 107 extends on the top surface and the side walls of the column-shaped spacer 143 as well as on the common electrode layer 106. The orientation film 107 is exposed to the liquid crystal layer 113. The orientation film 107 over the top surface of the column-shaped spacer 143 is in contact with the thin film transistor substrate 131. As described above, the column-shaped spacer 143 is provided in the gap between adjacent two of the pixels. Namely, the plural column-shaped spacers 143 are provided over the color filter substrate 111, so that the column-shaped spacers 143 form the inter-space defined between the color filter substrate ill and the thin film transistor substrate 131, so as to allow the liquid crystal layer 113 to fill the inter-space.
Another conventional structure of the liquid crystal display with the color filter substrate including column-shaped spacers will be described with reference to the drawings. FIG. 2A is a fragmentary schematic plan view of another conventional structure of the color filter substrate included in the conventional liquid crystal display. FIG. 2B is a fragmentary schematic cross sectional elevation view, taken along an X—X′ line in FIG. 2A, illustrative of the conventional structure of the conventional liquid crystal display.
A difference of this other conventional structure of FIGS. 2A and 2B from the above-described conventional structure of FIGS. 1A and 1B is only in that not only the column-shaped spacer 143 is provided over the top surface of the color filter layer 123 but further column-shaped spacers 144 and 145 are also provided over the top surfaces of the color filter layers 124 and 125. Namely, in accordance with the conventional structure of FIGS. 2A and 2B, a set of the three column-shaped spacers 143, 144 and 145 is provided in the gap between the adjacent two of the pixels.
The above-described conventional structure of FIGS. 1A and 1B has the following problem with temperature variation. FIG. 3A is a fragmentary schematic cross sectional elevation view illustrative of the conventional structure of the liquid crystal display shown in FIGS. 1A and 1B, wherein the display is placed at a normal temperature of, for example, 20° C. FIG. 3B is a fragmentary schematic cross sectional elevation view illustrative of the conventional structure of the liquid crystal display shown in FIGS. 1A and 1B, wherein the display is placed at a high temperature of, for example, 60° C.
The variation in temperature causes a variation in cell gap of the display. The cell gap is defined to be a distance in vertical direction between the bottom surface of the thin film transistor substrate 131 and the top surface of the orientation film 107 in the gap between the adjacent two of the color filter layers 123, 124 and 125. Namely, the cell gap corresponds to a maximum gap in vertical direction of the inter-space between the thin film transistor substrate 131 and the color filter substrate 111.
As shown in FIG. 3A, if the display is placed in the normal temperature environment, for example, at 20° C., a cell gap “T1” is given by a spacer 103 which is defined between the top surface of the orientation film 107 over the top surface of the column-shaped spacer 143 and the top surface of the orientation film 107 in the gap between the adjacent two of the color filter layers 123, 124 and 125. Namely, the height of the spacer 103 corresponds to a sum of a height of the column-shaped spacer 143 and a height of the color filter layer 123. Accordingly, in the normal temperature environment, the cell gap “T1” is given by the total height of the column-shaped spacer 143 and the color filter layer 123.
As shown in FIG. 3B, if the display is placed in the high temperature environment, for example, at 60° C., a cell gap “T2” is formed which is larger than the cell gap “T1”, because the top surface of the orientation film 107 over the top surface of the column-shaped spacer 143 is distanced from the bottom surface of the thin film transistor substrate 131. Namely, the temperature increase causes an expansion of the liquid crystal layer 113. This expansion of the liquid crystal increases the cell gap and distances the top surface of the orientation film 107 over the top surface of the column-shaped spacer 143 from the bottom surface of the thin film transistor substrate 131, whereby the thin film transistor substrate 131 is floated by the expanded liquid crystal layer 113 from the column-shaped spacer 143. Therefore, the cell gap “T2” is unstable and variable.
In order to avoid the last-described problem, it was proposed that in the normal temperature environment, the column-shaped spacer 143 be compressed in the vertical direction, so that in the high temperature environment, the column-shaped spacer 143 is allowed to be free of the vertical compression and returned to the original shape by the expansion of the liquid crystal layer 113, whereby the compression-free column-shaped spacer 143, however, still supports the thin film transistor substrate 131. The description of this alternative proposal will be made in detail with reference to the drawings.
FIG. 4A is a fragmentary schematic cross sectional elevation view illustrative of the conventional structure of the liquid crystal display shown in FIGS. 1A and 1B, wherein the display is placed at the normal temperature of, for example, 20° C., and the column-shaped spacer is compressed in the vertical direction. FIG. 4B is a fragmentary schematic cross sectional elevation view illustrative of the conventional structure of the liquid crystal display shown in FIGS. 1A and 1B, wherein the display is placed at a high temperature of, for example, 60° C., and the column-shaped spacer is free from any vertical compression.
In the normal temperature environment, as shown in FIG. 4A, the column-shaped spacer 143 is compressed in the vertical direction, so that a smaller cell gap “t1” is formed, which is smaller than the above cell gap “T1” shown in FIG. 3A. The column-shaped spacer 143 has an elasticity.
If the display is placed into the high temperature environment as shown in FIG. 4B, then the liquid crystal layer 113 is expanded to press the color filter substrate 111 and the thin film transistor substrate 131 outwardly, so that the vertical compression to the column-shaped spacer 143 is reduced, and thus a larger cell gap “t2” is formed which is larger than the above cell gap “t1” in the normal temperature environment. However, in the high temperature environment as shown in FIG. 4B, the compression-reduced column-shaped spacer 143 sill supports the thin film transistor substrate 131, whereby the thin film transistor substrate 131 is securely and stably supported by the compression-reduced column-shaped spacer 143. The cell gap “t2” is also stable and not variable. This technique is to utilize the elasticity of the column-shaped spacer 143.
FIG. 5A is a fragmentary schematic cross sectional elevation view illustrative of the conventional structure of the liquid crystal display shown in FIGS. 1A and 1B, wherein the display is placed at the normal temperature of, for example, 20° C. FIG. 5B is a fragmentary schematic cross sectional elevation view illustrative of the conventional structure of the liquid crystal display shown in FIGS. 1A and 1B, wherein the display is placed at a low temperature of, for example, −20° C.
As shown in FIG. 5A, if the display is placed in the normal temperature environment, for example, at 20° C., a cell gap “L1” is given by the spacer which is defined between the top surface of the orientation film 107 over the top surface of the column-shaped spacer 143 and the top surface of the orientation film 107 in the gap between the adjacent two of the color filter layers 123, 124 and 125. The column-shaped spacer 143 is free of any substantive vertical compression. Namely, the height of the spacer 103 corresponds to a sum of the height of the column-shaped spacer 143 and the height of the color filter layer 123. Accordingly, in the normal temperature environment, the cell gap “L1” is given by the total height of the compression-free column-shaped spacer 143 and the color filter layer 123.
As shown in FIG. 5B, if the display is placed in the low temperature environment, for example, at −20° C., then a cell gap “L2” is formed which is smaller than the cell gap “L1”, because the liquid crystal layer 113 is contracted and reduced in volume and thus the column-shaped spacer 143 is thus compressed in the vertical direction. The column-shaped spacer 143 is provided for the gap between the adjacent two of the pixels. Since the number of the column-shaped spacer 143 is small, then the total elastic force of the plural column-shaped spacers 143 is still smaller than the contracting force of the liquid crystal layer 113.
FIG. 6A is a fragmentary schematic cross sectional elevation view illustrative of the conventional structure of the liquid crystal display shown in FIGS. 2A and 2B, wherein the display is placed at the normal temperature of, for example, 20° C. FIG. 6B is a fragmentary schematic cross sectional elevation view illustrative of the conventional structure of the liquid crystal display shown in FIGS. 2A and 2B, wherein the display is placed at a low temperature of, for example, −20° C.
As shown in FIG. 6A, if the display is placed in the normal temperature environment, for example, at 20° C., a cell gap “L1” is given by the spacer which is defined between the top surface of the orientation film 107 over the top surface of the column-shaped spacers 143, 144 and 145 and the top surface of the orientation film 107 in the gap between the adjacent two of the color filter layers 123, 124 and 125. The column-shaped spacers 143, 144 and 145 are free of any substantive vertical compression. Namely, the height of the spacer 103 corresponds to a sum of the height of each of the column-shaped spacers 143, 144 and 145 and the height of each of the color filter layers 123, 124 and 125. Accordingly, in the normal temperature environment, the cell gap “L1” is given by the total height of each of the compression-free column-shaped spacers 143, 144 and 145 and each of the color filter layers 123, 124 and 125.
As shown in FIG. 6B, if the display is placed in the low temperature environment, for example, at −20° C., then a cell gap “L2” is formed which is nearly equal to the cell gap “L1”, because the liquid crystal layer 113 has a contracting force but not reduced in volume and thus the column-shaped spacers 143, 144 and 145 are not compressed in the vertical direction. The column-shaped spacers 143, 144 and 145 are provided for the gap between the adjacent two of the pixels. Since the number of the column-shaped spacers 143, 144 and 145 is large, then the total elastic force of the plural column-shaped spacers 143, 144 and 145 is larger than the contracting force of the liquid crystal layer 113. For this reason, the cell gap is not varied substantially. However, the liquid crystal layer 113 causes an evaporation of chemically unstable low molecular materials therein, whereby undesired bubbles or foam are formed in the liquid crystal layer 113. These bubbles or foam cause defects in the display device. Consequently, the small number of the column-shaped spacers is preferable for avoiding the undesired formation of the bubbles or foam in the liquid crystal layer 113.
The following descriptions will focus on how the status of the display device is changed upon application of an external load and after released from the load. FIG. 7A is a fragmentary schematic cross sectional elevation view of the liquid crystal display device shown in FIGS. 1A and 1B, prior to any application of external load. FIG. 7B is a fragmentary schematic cross sectional elevation view of the liquid crystal display device shown in FIGS. 1A and 1B, upon application of an external load in the vertical direction to the surface of the thin film transistor substrate. FIG. 7C is a fragmentary schematic cross sectional elevation view of the liquid crystal display device shown in FIGS. 1A and 1B, after released from the applied external load.
As shown in FIG. 7A, the liquid crystal display device before application of any external load is placed in the same state as that shown in FIGS. 1A and 1B, wherein the column-shaped spacer 143 is free of any compression, and the device has the originally designed cell gap “L1”.
As shown in FIG. 7B, the liquid crystal display device is applied with the external load in the direction vertical to the surface of the thin film transistor substrate 111, so that the column-shaped spacer 143 is compressed and largely deformed, and the device has a reduced cell gap “L2” which is smaller than the originally designed cell gap “L1”.
As shown in FIG. 7C, even after the liquid crystal display device is released from the external load, the column-shaped spacer 143 still remains in the deformed or compressed state, but not returned to the original shape, and thus the device remains having the reduced cell gap “L2”.
FIG. 8A is a fragmentary schematic cross sectional elevation view of the liquid crystal display device shown in FIGS. 2A and 2B, prior to any application of external load. FIG. 8B is a fragmentary schematic cross sectional elevation view of the liquid crystal display device shown in FIGS. 2A and 2B, upon application of an external load in the vertical direction to the surface of the thin film transistor substrate. FIG. 8C is a fragmentary schematic cross sectional elevation view of the liquid crystal display device shown in FIGS. 2A and 2B, after released from the applied external load. As a result, the cell gap variation is caused, and the display defect may be caused.
As shown in FIG. 8A, the liquid crystal display device before application of any external load is placed in the same state as that shown in FIGS. 2A and 2B, wherein the column-shaped spacers 143, 144 and 145 are free of any compression, and the device has the originally designed cell gap “L1”.
As shown in FIG. 8B, the liquid crystal display device is applied with the external load in the direction vertical to the surface of the thin film transistor substrate 111, so that the column-shaped spacers 143, 144 and 145 are compressed and slightly deformed, and the device has a reduced cell gap “L2” which is smaller than the originally designed cell gap “L1”.
As shown in FIG. 8C, after the liquid crystal display device is released from the external load, the column-shaped spacers 143, 144 and 145 become free from the deformed or compressed state, and are returned to the original shape, so that the device has again the originally designed cell gap “L1”. As a result, no cell gap variation is caused, nor display defect may be caused.
Consequently, increasing the density or the number of the column-shaped spacers may increase the mechanical resistivity to the externally applied load, but also allows undesired formation of bubbles or foam in the liquid crystal layer upon the temperature drop.
In the above circumstances, the development of a novel liquid crystal display with an improved spacer structure free from the above problems is desirable.